Centrifuge



J. STUART II:

Oct. 18, 1955 CENTRIFUGE 5 Sheets-Sheet 1 Filed Nov. 27, 1951 JOSEPHSTUARTH W q. PM

AGENT.

J. STUART II Oct. 18, 1955 CENTRIFUGE 5 Sheets-Sheet 2 Filed Nov. 27,1951 MQE AGENT.

J. STUART IE CENTRIFUGE Oct. 18, 1955 5 Sheets-Sheet 3 Filed Nov. 271951 JOSEPH STUART g INVENTOR.

AGENT.

Oct. 18, 1955 STUART 11 2,720,982

CENTRIFUGE Filed Nov. 27, 1951 5 Sheets-Shaw?- 4 45 Q J I 43 FIG- 9JOSEPH STUAR'T U INVENTOR.

BY PM AGENT.

J. STUART III Oct. 18, 1955 CENTRIFUGE 5 Sheets-Sheet 5 Filed Nov. 27,1951 JOSEPH STUART l law 516 AGENT.

2,720,982 Patented Oct. 18, 1955 CENTRIFUGE Joseph Stuart H, Wilmington,Del., assignor to Hercules Powder Compan Wilmington, Del., a corporationof Delaware Application November 27, 1951, Serial No. 258,392 2 Claims.(Cl. 210-68) This invention relates to an apparatus and process forseparating liquids from solid material. In a specific aspect thisinvention relates to an apparatus and process for separating spentnitrating acid from nitrocellulose and then washing the separatednitrocellulose.

Centrifuges of various types have been employed heretofore to separateliquids from solid material. In many instances the centrifuges employedhave been of the batch type, and in order to decrease the operatingcosts of the apparatus, efforts have been made to improve upon thebatch-type centrifuges and to construct a continuous type of centrifuge.One continuous type has employed a scraping or peeling knife within theseparating drum in order to provide for continuous removal of separatedmaterial from the drum. Another type of continuous centrifuge hasachieved continuous operation by providing means for axially moving theperipheral wall of the separating drum over an annular wall or walls inorder to obtain automatic discharge of the separated solid material fromthe centrifuge. The various centrifuges employed heretofore have hadobvious disadvantages, particularly when employed in such opertaions asthe nitration of cellulose Where the nitrated cellulose is separatedfrom spent nitrating acid by centrifuging and then washed free ofremaining spent nitrating 'acid by a series of water washes.

Conventional practice in the manufacture of nitrocellulose involvestreating, for example, cotton with nitrating acid for a desired periodof time by a batch procedure. Upon completion of the nitration, thedischarge valve of the nitrator is opened and the reaction mixture israpidly metered into a centrifuge which is brought up to the necessaryspeed for removal of acid from the nitrated cellulose. Spent acid is runby gravity from the outer jacket of the centrifuge to suitable recoveryequipment.

The centrifuge is stopped and the nitrocellulose is manually forked outthrough the bottom of the centrifuge and drowned in a water immersionbasin below. The manual handling of the nitrocellulose and the delayincident to discontinuous operation are objectionable, and the stoppingof the centrifuge to fork out the nitrocellulose requires excessive timeand causes too much delay for highest quality of product.

It is an object of this invention to provide a novel apparatus andmethod for separating solids from liquids.

.It is another object of this invention to provide a novel apparatus andmethod for separating cellulose derivatives from liqiud medium employedin the preparation of said cellulose derivatives.

It is a further object of this invention to provide a novel apparatusand method for separating nitrocellulose from spent nitrating acidobtained during the preparation of said nitrocellulose and for washingsaid nitrocellulose.

Further and additional objects and advantages of this invention will beapparent from the detailed disclosure hereinbelow.

The objects and advantages of this invention will be clearly apparentfrom the detailed description of the apparatus shown on the accompanyingdrawings and the operations thereof with reference symbols referring tolike parts wherever they occur.

. Apparatus Fig. 1' is anelevati'onal view of the apparatuswith thereciprocating piston in its inactivated position.

Fig. 2 is a plan view of the apparatus through section 2-2.

Fig. 3 is an enlarged elevational view of the centrifuge basket andaccompanying equipment with the reciprocating piston in its activatedposition.

Fig. 4 is an enlarged plan view of the reciprocating piston throughsection 44.

Fig. 5 is an enlarged elevational view of the reciprocating piston inits inactivated position through section Fig. 6 is an enlarged plan viewof the bottom or base of the centrifuge basket through section 66.

Fig. 7 is an enlarged elevational view of a section of the bar screen orinternal side wall of the centrifuge basket.

Fig. 8 is an enlarged plan view of a section of the bar screen-0n theinterior of the centrifuge basket.

Fig. 9 is an enlarged elevational view through section Fig. 10 is anelevational view of the feeding mechanism for the apparatus.

Fig. 11 is a plan view of the feeding mechanism through section'11-11.

Fig. 12 is an enlargedview of the centrifuge basket and accompanyingequipment with the reciprocating piston in its inactivated position anddepicting an alternative slurry distributor and splash sleevearrangement.

Referring now to the accompanying drawings, Fig. 1

'is an elevational view of a centrifuge that can be.used

to effect the desired separation of liquids and solids. The centrifugeshown in Fig. 1 contains a foraminous or per forate basket supported anddriven by rotor shaft 1. Rotor shaft 1 is attached to and operated by adriving mechanism not shown, and the lower portion of rotor shaft 1, asshown on Fig. 1, is combined with the necessary bearings, packings,snubbers, snubbe'r rings, oil and grease lines, and the like, for theoperation of rotor shaft 1. Since this equipment is conventional andsince it does not form a part of the invention, a detailed descriptionthereof is not necessary for an understanding of the invention. However,this conventional equipment is maintained free of corrosive fluids suchas acid fumes by air line 2. Air under pressure is continually passedthrough line 2 and in this manner the entrance of corrosive fluids tothe critical mechanism surrounding shaft 1 is prevented.

Rotor shaft 1 is attached to cylindrical casing 3 which is capped bystop nut 4. Surrounding casing 3 and contiguous thereto is a secondcylindrical casing 5 which is rigidly attached to and moves inconjunction with a rotor piston which is inside the basket of thecentrifuge and which will be described in detail infra.

Rotor bottom 6 which forms the bottom of the centrifuge basket isrigidly attached to casing 3 at its inner extremity, and at its outerextremity it is rigidly attached to the upwardly or vertically disposedside wall 7 of the centrifuge basket. The upper portion of side wall. 7is perforated to permit the passage of separated liquids therethroughwhile retaining separated solids on the inner surface of the verticalside wall. Disposed above rotor bottom 6 is rotor piston 8 which on itslower or bottom side contains a plurality of indentations which surroundand thus mesh with elevated and upwardly extending sections 6A of rotorbottom 6. Attached to the upper surface of rotor piston'8 is rotorpiston face 9 which moves irrconjunction with piston 8, but; if desired,piston face 9 and piston 8 can be combined and made integral to form therotor piston for the apparatus.

The upper portion of the centrifuge side wall 7 is perforated in orderto permit the passage of liquid through the side wall. The actualconstruction ofthe side wall will depend upon such variables as theultimate use of the centrifuge and the liquids andsolids to beseparated. A suitable perforated side wall for the separation of spentnitrating acid from a slurry thereof 'with nitrocellulose has been foundto include an outer casing containing a plurality of small openings.Within the outer casing and attached thereto is a screen formed byplacing a plurality of vertically disposed metallic bars at regularlyspaced distances around the inner surface of the outer casing. Thispreferred foraminous sidewall will be described in greater detail byreference to Figs. 7, Sand 9.

Surroundingcylindrical casing and forming an annular space therewith isa third cylindrical casing 10 which is rigidly attached to rotor pistonface 9. Attached to both casing 10 and rotor piston face 9 is slurrydistributor 11 which is eoncavely shaped and which directs the flow ofthe incoming slurry feed toward the side wall of the rotor basket whenthe centrifuge is in operation. Disposed above casing 10 and attached tothe upper extremity thereof is a frusto-conical casing 12 surroundingthe lower portion of the activating liquid tube tobe described infra;Since both casing 10 and distributor 11 are attached to piston face 9,these members, as well as casing 12, move in conjunction with pistonface 9.

[The upper portion of the centrifuge is provided with fume tube 13 forremoving undesirable fumes from the centrifuge and with activatingliquid tube 14 for introduction of the liquid necessary for thehydraulic operation of piston 8 and movement of suitably attachedmembers. Tube 14 extends downwardly into casing 12 and it is'providedwith a second tube 15 of smaller diameter for additional removal of airand fumes displaced from the nitrocellulose. Tube 15 communicates withtube 13 through connecting line 16. Extending downwardly into thecentrifuge and with their lower extremities within the cylindrical sidewall of the centrifuge are a plurality of-tubes 17, "18, 19 20, 21 and22 for the introduction ofwash liquids to the centrifuge. The lowerextremities ofthese wash tubes are at varying levels'and spaced so thatthe separated solids in'the form ofa layer or mat on the inner periphery'of-the side wall of the centrifuge can be subjected to a plurality ofwashings. The centrifu ge is provided with cover 23 to which areattached a pluralityof splash sleeve hangers'24. Hangers 24 extenddownwardly into the centrifuge, and at their lower extremities theyare'attached to splash sleeve 25 which forms an annular space withslurry distributor lljfor passage of the feed slurry to the centrifuge.Perforate blowoutpanel 40 is disposed between cover 23'and. curb 26.

Disposed outside the centrifuge basket are a plurality of curbs 26,27,28, 29, 30, 31 and 32 for removal of separated solid material,separated liquids and wash liquids. Separated solids are'removed viaoutlet 33 and the separated liquid and wash liquids are removed bysuitable outlets provided between the lower extremities of the curbs.Typical curb outlets for liquid removal are-shown on the drawing asoutlets 34 and 35. Water or other suitable inert liquid is introduced tothe base of the centrifuge via inlet 36.

The lower portion of side wall 7 is provided with a plurality of thiefvalves 37 and a second plurality of openings 38. The importance of andthe necessity for these openings in side wall 7 will be more fullyexplained in the subsequent discussion of the operation of thecentrifuge.- Opening 39 in rotor piston 8 permits the lubrication of theadjoining surfaces of side wall 7 and piston 8-and piston face 9 by theactuating liquid.

Fig. 2 is a plan view through section 22. This figure shows the relativelocations of wash pipes 17, 18,19," 20,

21 and 22. Fig. 2 also shows the location of splash sleeve 25 which iscylindrically shaped and flared at its lower extremity. Splash sleeve 25is connected to cover 23 by three vertically disposed splash sleevehangers 24 extending downwardly into the centrifuge. Splash sleeve 25 ismaintained motionless by its attachment to hangers 24. Sleeve 25 doesnot revolve when the centrifuge is in operation and it does not move inconjunction w'itli the hydraulic activation and deactivation of rotorpiston 82 Fig. 3 is an enlarged elevational view of the centrifugeshowing rotor piston 8 in its activated position. Rotor piston 8 isactivated by the introduction of activating liquid through activatingliquid tube 14 and thence via the annular space between casing 5 andcasing 10. The rotation and acceleration of the mass of activatingliquid hydraulically elevates rotor piston 8 and attached rotor pistonface 9 to the point where cylindrical casing 5 approaches but preferablyavoids actually contacting stop nut 4 and to the point where the lowerextremity of. rotor piston 8 at least partially uncovers opening 38.

Since activating liquid is removed via opening 38 to halt the upwardmovement of cylindrical casing 5, the position of rotor piston 8, asshown in Fig. 3, is one of complete activation. In this position ofcomplete activation rotor piston 8 has been elevated substantially abovethe elevated sections 6A of rotor bottom 6, but the indenta-- tions inrotor piston 8 still partially mesh with the ele,

vated portions 6A of rotor bottom 6, i. e., the lower extremity of rotorpiston 8 is slightly below the upper extremity of the elevated sections6A of rotor bottom 6;:-

Fig. 3 also shows the relative position of slurry distributor 11 andsplash sleeve 25 when rotor piston 8 and rotor piston face 9 are in aposition of complete activation. Additionally, Fig. 3 depicts therelative positions of the lower extremities of the six wash pipes. Thesewash pipes are positioned so as to wash the separated solid materialadjacent to the side wall of the centrifuge'at various levels as theseparated solid material is pushed upwardly along the centrifuge sidewall in the form of amat or layer thereon by the operation of rotorpiston 8 Fig. 5 is an enlarged elevational view through section 55showing rotor piston 8 and rotor piston face 9 in an inactivatedposition. Fig. 4 is an enlarged plan view of rotor piston 8 throughsection 4-4,'and Fig. 6 is an enlarged plan view of rotor bottom 6 withits plurality of elevated sections 6A which mesh with and fit into theplurality of indentations in the base of rotor piston 8. In order toactivate rotor piston 8, activating liquid, after introduction via tube14 and the annular space between casing 5 and casing 10, passes viaopenings in rotor piston 8. This activating liquid then enters thespaces between the elevated sections 6A of rotor bottom 6 and theindentations in rotor piston 8. The-activating liquid in these spacesexerts the force imparted to it by the centrifugal action of theapparatus,.and, consequently, rotor piston 8 is moved upwardly. Rotorpiston 8 is then in an activated position and it assumes a position ofdeactivation as the activating liquid is removedfrom the piston viaopenings 38 and thief valves 37.

Fig. 7 is an enlarged elevational viewof the foraminous portion of sidewall 7. It will be'understoodthat the construction of side wall 7 willbe determined by a con-; sideration of various factors, and the type ofconstruction desired will depend to a large extent upon the centrifugalforce to be exerted upon it and upon the liquids and solids in theslurry to be resolved. cellulose from spent nitrating acid it was founddesirableto employ anouter perforate casing with a bar screen ofvertically extending metallic bars disposed along the inner periphery ofthe outer casing. Fig. 7 depicts the 7 upper portion of side wall 7comprised of outer'perfora'te l casing 41, containing a series ofperforations or openings 42, and of inner perforate bar screen 43. Barscreen In order to separate nitro- 43 is composed of a plurality ofvertically disposed metallic bars 44 spaced at regular intervals aroundthe inner periphery of perforate casing 41. The individual bars 44 arerigidly maintained in place by a plurality of circular metallic rings 45each disposed in a horizontal plane. Fig. 8 is an enlarged plan view ofmetallic bars 44 and circular ring 45, and Fig. 9 is an enlargedelevational view through section 99 showing metallic bar 44 and circularring 45.

Fig. 10 is an elevational view of the feeding unit that was foundeffective for introducing the slurry feed to the centrifuge. Fig. 10also shows the preferred relative position of the feeding unit withother members of the centrifuge such as activating liquid tube 14,splash sleeve and slurry distributor 11. The feeding unit consists of acylindrical inlet tube 51 through which the feed slurry enters feederbox 52. Thence the feed slurry enters the centrifuge via the base offeeder box 52 and the annular space between splash sleeve 25 and slurrydistributor 11. Fig. 11 is a plan view of the base of feeder box 52showing opening 53 through which the feed slurry enters the centrifuge.The cross-sectional area of opening 53 corresponds substantially withthe cross-sectional area of feeder tube 51 to provide for even andunhindered flow of feed slurry through the feeding unit and into thecentrifuge.

Fig. 12 is an enlarged elevational view showing rotor piston 8 in itsactivated position and showing an alternative slurry distributor andsplash sleeve. In this drawing slurry distributor 11A is substantiallystraight on approximately a degree angle, and it does not have the cancave curvature of distributor 11 in Fig. 3. Distributor 11A is rigidlyattached to rotor piston face 9 and to casing 10, and distributor 11Amoves in conjunction with those members to which it is attached. Splashsleeve 25A, which is disposed on about a 75 degree angle with thehorizontal, forms an annular space with distributor 11A, and it isthrough this annular space that feed slurry is introduced to theseparating action of the centrifuge. Sleeve 25A at its upper extremityis attached to and moves in conjunction with casing 10, and,consequently, the position of sleeve 25A relative to distributor 11Aremains unchanged during the operation of the centrifuge. The slurrydistributor and splash sleeve shown in Fig. 3 are described in detailand claimed in the copending application, Serial No. 258,364, filedNovember 27, 1951.

It will be understood that the apparatus described above in detail haswide application for the separation of a slurry of liquid and solidmaterial. One application for which the apparatus is particularlysuitable is for the separation of nitrocellulose from spent nitratingacids that are obtained during the nitration of cellulosic material. Itis a preferred application of this apparatus to effect such a separationof nitrocellulose from spent nitrating acid, and the actual operation ofthe apparatus will be described in detail employing a feed slurry ofnitrocellulose and spent nitrating acids from a cellulose nitrationprocess.

Operation To initiate the separation, the operation of the centrifuge isbegun by the driving mechanism (not shown) operating on shaft 1 which inturn effects the revolution of the centrifuge basket and accompanyingmembers. It Will be understood that the centrifuge can be operated at aspeed suitable for effecting the necessary separation. With a feedslurry of nitrocellulose and spent nitrating acids and with a centrifugebasket having a diameter of about 23 inches a minimum speed of 700800 R.P. M. can be employed, and the maxmum preferred speed has been found tobe about 1700 R. P. M. With the centrifuge at the desired speed and withthe rotor piston in the inactivated position as shown in Fig. 1 and Fig.5, a measured quantity of feed slurry is introduced to the apparatus viafeeding tube 51. The feed slurry passes through feeding box 52containing slot or opening 53 and it then passes through the annularspace between splash sleeve 25 and distributor 11. Since the centrifugeis revolving rapidly, the feed slurry is accelerated and transferredtoward bar screen 43 along the inner periphery of side wall 7. Foreffective separation of a slurry of nitrocellulose and spent nitratingacid it is preferred that the maximum space between the metallic bars ofbar screen 43 be no greater than 0.01 inch. The operation of thecentrifuge is continued and spent nitrating acid is forced out of thenitrocellulose while the latter is retained in a mat on the innersurface of the bar screen. The spent nitrating acid passes through thebar screen and through openings 42 in perforated casing 41 surroundingthe bar screen, and after passage along curb 32 it is recovered forfurther use. After a sufficient period of time has elapsed for removalof spent nitrating acid from the solid nitrocellulose, activating liquidis introduced to the centrifuge via tube 14. This activating liquid maybe any liquid, preferably compatible with the spent nitrating acid, thatwill provide suitable hydraulic operation of piston 8 and the actualliquid that is employed will vary with the separation that is beingeffected by the centrifuge. In some instances water will be found to bea suitable activating liquid. For the separation of nitrocellulose fromspent nitrating acid a portion of the spent nitrating acid itself can beused as the activating liquid. Thus, in the preferred operation beingdescribed, a predetermined quantity of spent nitrating acid enters thecentrifuge via tube 14 and it passes through the annular space betweencasing 5 and casing 10. Then it passes through openings in piston 8 andit enters the space between the indentations in piston 8 and theelevated sections 6A of bottom plate 6. The activating liquid builds upsufficient pressure, due to the centrifugal action, to hydraulicallyelevate piston 8, and consequently the movement of piston 8 and attachedpiston face 9 effects an upward movement of the mat of nitrocellulose onthe bar screen equivalent in distance to the length of stroke of piston8. The activating liquid causes the movement of piston 8 sufficient tobring the lower extremity of that piston in such a position thatopenings 38 in side wall 7 are at least partially uncovered, andactivating liquid then escapes through openings 38. Thus, the upwardmovement of rotor piston 8 is controlled by escape of the activatingliquid and by the volume of activating liquid employed. Any number ofopenings in side wall 7 corresponding to opening 38 can be used toeffect the desired removal of activating liquid. Actually, in operationtwenty-four openings have been employed, but this number can be widelyvaried, and the number used will depend upon the actual size of theindividual openings. During the activation of rotor piston 8, thiefvalves 37 in side wall 7 are open continuously, and consequentlyactivating liquid is continuously escaping through these valves. Thearea of these valves is considerably less than the area of openings 38,and the area of valves 37 is adjusted to effect the desired lowering orinactivation of rotor piston 8 in a predetermined time interval. Theupper limit of the stroke of piston 8 is determined by the position ofopenings 38, and the rate of release of activating liquid through valves37 determines the speed at which rotor piston 8 is returned to itsinactivated position. The number of thief valves that is necessary forthe efiicient operation of the centrifuge is variable over relativelyWide limits. In operation eight thief valves corresponding to valve 37have been employed in side wall 7, but it will be seen that this numbercan be varied while remaining within the scope of the invention.

As rotor piston 8 begins its descent from its activated position to theinactivated position, a second measured quantity of feed slurry isintroduced to the centrifuge as previously described, and as spentnitrating acid is being removed from this second portion of feed slurrythe first portion of nitrocellulose introduced to the centrifuge iswashed with a sufiicient quantity of spent nitrating acid diluted toabout a concentration-and introduced 7 second feed portion,

greater number of washing steps 7 above will be found useful, while inother instances no via line. 17 to displace spent nitrating. acid, whichgener- Y ally has, a concentration in excess of 60%, remaining in themat of nitrocellulose. The latter is recovered after passage used as anactivating liquid or it can be subjected to suitable steps'for therecovery of the acids. Upon completion of a predetermined time intervalduring which the first portion of nitrocellulose is washed with 60% acidand s'pent nitrating acid is centrifugally wrung out of the anotherpredetermined amount of activating liquid is introduced to thecentrifuge as previously described to effect the upward movement ofrotor piston 8 and the mat of nitrocellulose being formed upon the innerwalls ofthe ,bar screen,

. Upon continued operation of the centrifuge as previously described, acontinuous mat of nitrocellulose is formed upon the inner surface of'thebar screen. As the nitrocellulose progresses upward along the barscreen, it is washed at various levels with varying concentrations ofspent nitrating acid. As already pointed out, the first washing waseffected with a 60% acid. The second washing can be effected with a 40%acid; the third washing with a 20% acid, and the final washing withwater. These acid concentrations are given merely by way of example, andit will be understood that other concentrations can be 'used withoutdeparting from the scope of the invention. The acidwhich is displacedfrom the nitrocellulose during each of the washings is recovered afterpassage along the respective curbings, and the recovered acids can thenbe recycled and used to carry out additional washing of thenitrocellulose mat inside the centrifuge. The final washing of thenitrocellulose is effected with water and subsequently the washednitrocellulose is sloughed over the top of the bar screen and side wall7 with an additional amount of water. This nitrocellulose and water passalong curbing 27 to the base of the centrifuge. Additional amounts ofwater are introduced to the centrifuge via inlet 36 to wash thenitrocellulose along the sloped base of the centrifuge and to remove thenitrocellulose via outlet 33. The nitrocellulose thus removed can thenbe separated from accompanying water by. any suitable process, and it isthen ready for any subsequent steps in the nitrocellulose manufacturingprocess.

The washing of the solid mat on the inner surface of the bar screen,'asdescribed above, is particularly useful in the separation ofnitrocellulose from spent nitrating add In effecting other separationsof, solid material from accompanying liquids, such washing steps may ormay not be necessary. In some instances a fewer or than those describedwashing steps will be required. It will be understood that the number ofwashing steps that are employed can'be' varied without departing fromthe scope of the invention and that it is within the scope and spirit ofthe invention to operate the centrifuge without any washing steps.Numerous other variations and modifications within the scope of theinvention will be apparent to those skilled inthe art from the detaileddisclosure above.

What I claim and desire to protect by Letters Patent is:

1, In a centrifuge for separating solid substances from liquids, avertically disposed drumrotatably mounted on a vertical drive shaft,said drum having an imperforate solid-base, an iinperforate cylindricalaxial hub attached to said drive shaft and extending upward interiorlyof said drum, and a perforate side wall on the inside surface of whichsolid substances accumulate in the form of a layer during centrifugalaction, said base having a plurality of elevated sections disposedinteriorly of said drum; a solid piston axially and slidably mounted onsaid hub within the drum and rotatable with said drum, said pistonhaving an imperforate cylindrical sleeve attached to its upper faceconcentrically disposed around said axial hub and spacedapartvtherefrorn to form an annular space, aplurality of openingscommunicating along curb 31, and it can be subsequently with the annularspace between said sleeve and said axial hub, and a plurality ofindentations in itslower horizontal surface that mesh with said elevatedsections of said drum base, said piston being movable axially upwardwhen activated to displace solid substances 'upwardly in the form of alayer on said side wall along the inner periphery of said side wall; andan inlet disposed above and communicating with the annular space betweensaid sleeve and said axial hub for introducing piston-activating liquidbetween said imperforate drum base and said'piston, said piston beingactivated axially upward solely by centrifugal force created by rotationof the centrifuge acting upon said activating liquid between saidimperforate drum base and said piston; said drum side wall having afirst plurality of openings of predetermined cross-sectional areadisposed in a horizontal plane immediately below the lower extremity ofthe piston at the upper limit of its upward stroke for rapid escape ofpiston-activating liquid and having a second plurality of openings of apredetermined crosssectional area disposed in a horizontal plane withthe lower extremity of said piston at the lower'limit of its stroke forslow escape of piston-activating liquid to con trol the rate of movementof said piston from the upper to the lower limit of its stroke;

2. In a centrifuge for separating solid substances from liquids, averticaly disposed drum rotatably mounted on a vertical drive shaft,said drum having an imperforate solid base, an imperforate cylindricalaxial hub attached to said drive shaft and extending upward interiorlyof' said drum, and a perforate side wall on the inside surface of whichsolid substances accumulate in the form. of a layer during centrifugalaction, said base having a pluralityof elevated sections disposedinteriorly of said drum; a solid piston axially and slidably mounted onsaid hub within the drum and rotatable with said drum, said pistonhaving an imperforate cylindrical sleeve attached to its upper faceconcentrically disposed around said axial hub and spaced apart therefromto form an annular space, a plurality of openings communicating with theannular space between said sleeve and said axial hub, and a plurality ofindentations in its lower horizontal surface that mesh with saidelevated sections of said drum base, said piston being movable axiallyupward when activated to displace solid substances upwardly in the formof a layer on said side wall along the inner periphery of said sidewall; an inlet disposed above and communicating with the annular spacebetween said sleeve and said axial hub for introducing piston-activatingliquid between said imperforate drum base and said piston, said pistonbeing activated axially upward solely by centrifugal'force created byrotation of the centrifuge acting upon said activating liquid betweensaid imperforate drum base and said piston; said drum side wall having afirst plurality of openings of'predetermined cross-sectional areadisposed in a horizontal plane immediately below the lower extremity ofthe piston at the upper limit of its upward stroke for rapid escape ofpiston-activating liquid and? having a second plurality of openings of apredetermined cross-sectional area disposed in a horizontal plane withthe lower extremity of said piston at the lower limit of its stroke forslow-escape of piston-activating liquid to control the rate of movementof said piston from'the References Cited in the file of this patentUNITED STATES PATENTS 1,382,142 Sturgeon June 21, 1921 1,928,341 T61Meer Sept. 26, 1933 (Other references on following page) Altpeter Jan.23, 1934 Walkup Dec. 6, 1949 Carnagua et a1 Oct. 9, 1951 Bryant Nov. 18,1952 Sollinger June 16, 1953 Cox et a1 July 21, 1953 10 FOREIGN PATENTSGreat Britain 1922 Great Britain Aug. 22, 1918 Great Britain Nov. 9,1922 France June 18, 1907 Germany Mar. 28, 1897

1. IN A CENTRIFUGE FOR SEPARATING SOLID SUBSTANCES FROM LIQUIDS, A VERTICALLY DISPOSED DRUM ROTATABLY MOUNTED ON A VERTICAL DRIVE SHAFT, SAID DRUM HAVING AN IMPERFORATE SOLID BASE, AN IMPERFORATE CYLINDRICAL AXIAL HUB ATTACHED TO SAID DRIVE SHAFT AND EXTENDING UPWARD INTERIORLY OF SAID DRUM, AND A PERFORATE SIDE WALL ON THE INTERIORLY OF OF WHICH SOLID SUBSTANCES ACCUMULATE IN THE FORM OF A LAYER DURING CENTRIFUGAL ACTION, SAID BASE HAVING A PLURALITY OF ELEVATED SECTIONS DISPOSED INTERIORLY OF SAID DRUM; A SOLID PISTON AXIALLY AND SLIDABLY MOUNTED ON SAID HUB WITHIN THE DRUM AND ROTATABLE WITH SAID DRUM, SAID PISTON HAVING AN IMPERFORATE CYLINDRICAL SLEEVE ATTACHED TO ITS UPPER FACE CONCENTRICALLY DISPOSED AROUND SAID AXIAL HUB AND SPACED APART THEREFROM TO FORM AN ANNULAR SPACE, A PLURALITY OF OPENINGS COMMUNICATING WITH THE ANNULAR SPACE BETWEEN SAID SLEEVE AND SAID AXIAL HUB, AND A PLURALITY OF INDENTATIONS IN ITS LOWER HORIZONTAL SURFACE THAT MESH WITH SAID ELEVATED SECTIONS OF SAID DRUM BASE, SAID PISTON BEING MOVABLE AXIALLY UPWARD WHEN ACTIVATED TO DISPLACE SOLID SUBSTANCES UPWARDLY IN THE FORM OF A LAYER ON SAID SIDE WALL ALONG THE INNER PERIPHERY OF SAID SIDE WALL; AND AN INLET DISPOSED ABOVE AND COMMUNICATING WITH THE ANNULAR SPACE BETWEEN SAID SLEEVE AND SAID AXIAL HUB FOR INTRODUCING PISTON-ACTIVATING LIQUID BETWEEN SAID IMPERFORATE DRUM BASE AND SAID PISTON, SAID PISTON BEING ACTIVATED AXIALLY UPWARD SOLELY BY CENTRIFUGAL FORCE CREATED BY ROTATION OF THE CENTRIFUGE ACTING UPON SAID ACTIVATING LIQUID BETWEEN SAID IMPERFORATE DRUM BASE AND SAID PISTON; SAID DRUM SIDE WALL HAVING A FIRST PLURALITY OF OPENINGS OF PREDETERMINED CROSS-SECTIONAL AREA DISPOSED IN A HORIZONTAL PLANE IMMEDIATELY BELOW THE LOWER EXTREMITY OF THE PISTON AT THE UPPER LIMIT OF ITS UPWARD STROKE FOR RAPID ESCAPE OF PISTON-ACTIVATING LIQUID AND HAVING A SECOND PLURALITY OF OPENINGS OF A PREDETERMINED CROSSSECTIONAL AREA DISPOSED IN A HORIZONTAL PLANE WITH THE LOWER EXTREMITY OF SAID PISTON AT THE LOWER LIMIT OF ITS STROKE FOR SLOW ESCAPE OF PISTON-ACTIVATING LIQUID TO CONTROL THE RATE OF MOVEMENT OF SAID PISTON FROM THE UPPER TO THE LOWER LIMIT OF ITS STROKE. 